This invention relates to hydraulic positioners in general and more particularly to an improved hydraulic positioner which permits faster operation of a valve.
In process or power generation plants, valves or other devices are frequently required which must open suddenly in the case of a failure or under certain other operating conditions. Such valves are necessary to permit a discharge or a bypass in order to prevent damage to the main plant or to insure an emergency supply to subsequent parts of a plant. For example, in some steam power plants there are auxiliary devices or consumers which normally utilize steam exhausted by a turbine. Should the turbine tripout operate to shut down the turbine, there is a need to continue supplying these consumers. Thus, fast operating valves are often connected in parallel with turbine tripout valves for this purpose.
In order to insure a realiable and rapid response of valves of this nature, a positioner is required, which, on one hand, keeps the valve securely closed but which, on the other hand, will open the valve without delay quickly and without trouble if the appropriate operating conditions are present.
In view of this, it is object of the present invention to provide a positioner which meets these requirements to the utmost, i.e. a positioner which automatically opens the valve with maximum speed and which can also reclose the valve automatically if necessary. Furthermore, a positioner which operates realible in all operating cases without the possibility, for example, of a different thermal expansion exerting an influence on the function of the positioner is required.